3,4-Ethylenedioxythiophene Explained

3,4-Ethylenedioxythiophene (EDOT) is an organosulfur compound with the formula C₂H₄O₂C₄H₂S. The molecule consists of thiophene, substituted at the 3 and 4 positions with an ethylene glycolyl unit. It is a colorless viscous liquid.^[1]

EDOT is the precursor to the polymer PEDOT, which is found in electrochromic displays, photovoltaics, electroluminescent displays, printed wiring, and sensors.^{[2] [3]}

Synthesis and polymerization

The original synthesis proceeded via the diester of 3,4-dihydroxythiophene-2,5-dicarboxylate.EDOT is often prepared from C4 precursors such as butanediol and butadiene via routes that produce the thiophene and dioxane rings in separate steps. Representative is the reaction of 2,3-butanedione, trimethyl orthoformate, and ethylene glycol to form the dioxane. Sulfidization with elemental sulfur gives the bicyclic target.^[4]

EDOT is converted into the conducting polymer PEDOT by oxidation. The mechanism for this conversion begins with production of the radical cation [EDOT]⁺, which attacks a neutral EDOT molecule followed by deprotonation. Further similar steps result in the dehydropolymerization. The idealized conversion using peroxydisulfate is shown

n C₂H₄O₂C₄H₂S + n (OSO₃)₂²⁻ → [C₂H₄O₂C₄S]_n + 2n HOSO₃⁻

For commercial purposes, the polymerization is conducted in the presence of polystyrenesulfonate.^[3]

References

1. Conductive Modifications of Polymers with Polypyrroles and Polythiophenes. Synthetic Metals. 41. Jonas, F. . Schrader, L. . 1991. 3. 831–836. 10.1016/0379-6779(91)91506-6.
2. Groenendaal, L. B. . Jonas, F. . Freitag, D. . Pielartzik, H. . Reynolds, J. R.. Poly(3,4-Ethylenedioxythiophene) and Its Derivatives: Past, Present, and Future. Adv. Mater.. 2000. 12. 7 . 481–494. 10.1002/(SICI)1521-4095(200004)12:7<481::AID-ADMA481>3.0.CO;2-C.
3. Kirchmeyer, S. . Reuter, K.. Scientific Importance, Properties and Growing Applications of Poly(3,4-Ethylenedioxythiophene). J. Mater. Chem.. 2005. 15. 21. 2077–2088. 10.1039/b417803n.
4. Hachiya, I. . Yamamoto, T. . Inagaki, T. . Matsumoto, T. . Takahashi, A. . Mizota, I. . Shimizu, M. . 3 . Two-Step Synthesis of 3,4-Ethylenedioxythiophene (EDOT) from 2,3-Butanedione. Heterocycles. 2014. 88. 607–612. 10.3987/COM-13-S(S)8. 2024-02-17 . free .